Conventionally, there is known a variable compression ratio mechanism arranged to vary an engine compression ratio of an internal combustion engine by using a multi-link piston crank mechanism.
For example, a patent document 1 discloses a variable compression ratio mechanism including a control shaft arranged to vary an engine compression ratio of an internal combustion engine in accordance with a rotation position; an arm portion extending from the control shaft in a radial direction; a lever rotatably linked through a link pin to the arm portion, and arranged to be reciprocated in the radial direction of the control shaft; an actuator arranged to drive the lever; and journal portions of the control shaft which are provided on both sides of the arm portion in an axial direction.
In this patent document 1, a thrust surface confronting an axial end surface of the link pin is provided to the control shaft, or a bearing member rotatably supporting the journal portions. The link pin is retained by this thrust surface.
However, a position of the link pin is varied by a rotation of the control shaft when the engine compression ratio is varied. Accordingly, it is necessary that the thrust surface is formed to the bearing member and the control shaft so that the thrust surface confronts the end surface of the link pin even when the engine compression ratio is varied.